Devices and methods for testing the energy measurement accuracy, billing accuracy, functional performance and safety of electric vehicle charging stations

ABSTRACT

Testing of electric vehicle charging stations (EVCS) is performed. In an active mode, the device provides or is connected with a programmable load capable of emulating the load of an electrical vehicle (EV). In passive mode, the load is an EV with the device being arranged in series between the EVCS and EV. In either case, energy delivery from the EVCS to the load is monitored by the device to determine energy measurement and billing accuracy of the EVCS. This enables a comparison to be made between a measured value of energy delivered and a metered value of energy delivered as given by the EVCS. Other measurements and safety tests may also be performed by the device. A programmable load controller is also provided for providing a variable effective load as seen by the EVCS based on one or more fixed loads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 14/489,724, which claims the benefit of U.S.Provisional Patent Application No. 62/003,296, filed May 27, 2014, thecomplete contents of both applications being herein incorporated byreference.

FIELD OF THE INVENTION

The invention pertains to testing the energy measurement and billingaccuracy, functional performance and safety of electric vehicle chargingstations (EVCS).

BACKGROUND

Pluggable electric vehicles (EVs) are rapidly growing in popularity. Tosupport these vehicles, electric vehicle charging stations (EVCS) arebeing introduced for use in homes, offices, and commercial locations.Initially these charging stations were no more than fancy plugs with aminimum of added functionality to ensure safe operation. The typicalenvisioned application was a wall mounted device located in the garageof a private home. There was no issue of the charging station needing tomeasure the energy provided to the vehicle. As pluggable electricvehicles have proliferated, different use scenarios have materialized.In many of these use scenarios, the user must be charged for the energydelivered to the vehicle. When these EVCSs are used in commerce, forexample as a paid public refueling station or in a submetering situationwhere the energy used for vehicle charging receives a different ratefrom the utility, the EVCS must measure energy accurately so as toprovide accurate information for a financial transaction (billing). Justas the gas pumps at filling stations are tested periodically to assurethat the customer is being fairly charged, EVCS used in commerce willneed to be tested for accurate delivery of electric energy.

Up to this point in time, existing technology developed for testing EVCSoperation has been concerned with the communication protocols by whichan EVCS exchanges information with an electric vehicle. US PatentApplication Publication No. 2013/0346010 A1 by Schulz, for example,discloses a testing system enabled to provide verification signals incompliance with existing charging protocols. Current, voltage, chargesequence, and power levels received from the EVCS may be determined.However, these measures alone as disclosed by Schulz can only servepurposes of ensuring that the charging of the electric vehicle isworking within an accepted performance envelope that is required by EVcharging standards. For example, Schulz's current measurement devicesassist in enabling the testing system to monitor power levels comingfrom the EV charger and to detect current leakages or other faults inthe power provided to the charger testing system. This is important, forexample, because determination of power levels ensures that an EVCS willnot overwhelm and damage an EV battery with a higher rate of powerdelivery than it is designed to withstand. A simple analogy is asmartphone battery which, if directly connected to a standard walloutlet without its power adapter, would burn up and be destroyed. Inthis scenario, Schulz would be concerned with examining the powerratings of the adapter to verify the smartphone battery is not exposedto too strong a current, voltage, or instantaneous power level whichwould cause damage.

Though systems such as Schulz are relevant to ensuring the safe andprotocol-compliant operation of an EVCS with an electric vehicle, theyare deficient in addressing energy measurement and billing accuracy.Said differently, there remains a deficiency in the field for a systemusable to verify whether EVCSs actually deliver a total amount of energywhich they claim to deliver and for which they therefore bill a customeroperating the EVCS to charge the battery of his or her EV.

SUMMARY

Some exemplary embodiments of the invention combine into a single toolall of the capabilities needed to verify safety, operation, andimportantly energy measurement accuracy.

The number of manufacturers producing electric vehicle charging stationsis rapidly growing. Standards on the charging connector and protocoldiffer from country to country and are evolving rapidly. In the UnitedStates all currently manufactured models of major car companies use theSAE J1772-201010 standard. However, a new version of the SAE J1772standard is currently in development which expands the number ofcharging methodologies and connectors.

An exemplary embodiment of the invention is a device for testingelectric vehicle charging stations (EVCSs) that combines into a singletool all of the capabilities needed to verify safety, operation, andenergy measurement accuracy. It differs from prior art in a number ofsignificant ways which may include but are not limited to:

-   -   (1) It is capable of being connected in a variety of manners        either as a standalone device (e.g., as shown in FIG. 1A), or in        series with a vehicle being charged (e.g., as shown in FIG. 2);    -   (2) It is capable of accurately measuring the energy delivered        by the EVCS to the electric vehicle (or internal load) or by the        electric vehicle to the EVCS;    -   (3) It is capable of automatically determining the energy which        the EVCS has measured as being delivered/received and comparing        that to the actual energy delivered/received;    -   (4) It measures one or more up to all of the following types of        energy: active energy (e.g., kWh), reactive energy (e.g.,        VAR-Hrs), and apparent energy (e.g., VA-Hrs);

An exemplary embodiment of the invention combines the unique featuresabove with functionality found in prior art to form a complete testsystem for all EVCS systems.

Standards and technologies in the Electric Vehicle Charging space arechanging very rapidly. Currently most new US electric vehicles use theSAE J1772-201010 connector and associated protocol. This combinationsupports AC charging at current levels up to 80 amps. Two levels ofcharging capacity are defined. AC Level 1 uses 120 VAC with currentlevels up to 16 amps. AC Level 2 uses 208 to 240 VAC with current levelsup to 80 amps though levels above 32 amps are not common as of thefiling of this application. The Society of Automotive EngineersInternational (SAE) is about to issue a new version which expands thecharging categories to include DC Level 1 (0-80 amps at 50 to 500 VDC)and DC Level 2 (0-200 amps at 50 to 500 VDC). DC Level 1 will use thesame connector as AC Levels 1 and 2; however, DC Level 2 will use a newDC Combo connector. Exemplary embodiments of the invention are intendedto address all existing, presently under development, and futureprotocols and connections which transfer power to the vehicle throughtwo power pins at a given time, optionally include a ground pin, and useinterlocks and a communication medium to allow the EVCS and vehicle tointeract. To meet the needs of a particular future EVCS approach,different embodiments for specific parts of the invention may berequired. However, such changes are believed to be within the scope ofanyone skilled in the art once the protocols are published and in viewof the teachings herein. For example, one embodiment for the presentJ1772 standard which uses AC power only may use a current transformer asthe current transducer, while a more comprehensive unit addressing ACLevel 1 & 2 and DC Level 1 may use a zero flux transformer despite itslarger size and greater cost. Alternatively, in this exemplary AC/DCembodiment a current shunt or active closed loop Hall effect transformermay be used if lower accuracy is acceptable in a particular application.The application of either is well understood in the field of powermeasurement.

Some exemplary embodiments of the invention allow testing in an activemode where they provide the load and protocols for testing or in apassive mode where they monitor the interaction between an electricvehicle and an EVCS. In either configuration the system may measure bothtotal energy delivered by the EVCS and metering accuracy.

According to another aspect of the invention, a flexible programmableload is provided which emulates the electric vehicle. While there existlong established techniques for AC/DC load control going back to U.S.Pat. No. 5,355,294 A by De Doncker and Kheraliwala, and more recent workin the field of lighting control as represented by U.S. Pat. No.8,111,009 B2 by Tsai, et al., a programmable load according to thepresent disclosure differs significantly in application and design.Generally, all of the devices in the prior art are focused on the signalas presented to the load. Generally there is no consideration as to thewaveforms only the power delivered on the load side. In exemplaryembodiments disclosed herein, the application is quite different. Anexemplary programmable load is provided which emulates an electricvehicle while meeting a requirement of presenting a nearly unity powerfactor load to the EVSE. To meet this requirement, the programmable loadtreats the waveform of its input as a significant parameter. A tunedfilter network is implemented around the chopping circuit. The tunedfilter network is optimized to provide a low distortion, substantiallyunity power factor load as seen by the EVSE. A programmable loadaccording to the present invention uniquely emulates an EV according toa combination of input waveform control and unity power factor load tothe EVSE.

According to an exemplary embodiment, testing of an EVCS (e.g., asdescribed above) is performed without distinct functional modes. Systemoperation is simplified in that the operator is not required to select adistinct mode. Rather, the system evaluates all of the availableconnections (e.g., to the EVSE, Programmable Load, or EV) and proceedsto perform all tests selected by the user as desirable provided they areapplicable to the detected configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic of a testing scenario involving an EVCS and adevice according to the invention which may include an internalprogrammable load or be attachable to a standalone programmable load;

FIG. 1B is a schematic of a testing scenario similar to that shown inFIG. 1A, except the programmable load has been broken into separatecomponents: a programmable load controller and a fixed resistive loadcapable of drawing the maximum desired current;

FIG. 2 is a schematic of a testing scenario involving an EVCS, a deviceaccording to the invention, and an electric vehicle which may serve asthe load;

FIG. 3 is a block diagram of an exemplary embodiment of a deviceaccording to the invention;

FIG. 4A is a sample embodiment using a current transformer, signalconditioning, and analog-to-digital converter (ADC);

FIG. 4B is sample embodiment of a voltage transformer, signalconditioning, and analog-to-digital converter (ADC);

FIG. 5 is a block diagram of the functionality of the digital processingmeans shown in FIG. 3;

FIG. 6 is example circuitry according to an exemplary embodiment;

FIG. 7 is an example sequence of events and signals occurring duringconnection and removal of a charging connection with an electricvehicle;

FIG. 8A provides an exemplary operational sequence for the TOTAL testmode;

FIG. 8B provides an exemplary operational sequence for the STANDARD testmode;

FIG. 8C provides an exemplary operational sequence for the DUAL testmode;

FIG. 8D provides an exemplary operational sequence for the PASSIVE testmode;

FIG. 9 provides an example block diagram for the programmable loadaccording to an exemplary embodiment;

FIG. 10 provides circuitry detail according to an exemplary embodimentof the load current controller and isolated gate driver of theprogrammable load shown in FIG. 9;

FIG. 11 presents a suite of waveform traces of the input current of theprogrammable load controller (output current of the EVSE) versus theduty cycle of the chopper circuit; and

FIG. 12 presents a plot of input current of the programmable loadcontroller (output current of the EVSE) versus chopper duty cycle for a3 ohm load.

DETAILED DESCRIPTION

As used herein, “electric vehicle (EV)” may refer to a vehicle which isentirely electric, such as the LEAF (trademark of Nissan) or a TeslaRoadster of Tesla Motors Inc., or a hybrid vehicle which is electricallypowered and supplemented by a gas powered engine. The term “electricvehicle charging station (EVCS)” may be used interchangeably with otherknown industry terms such as “electric vehicle supply equipment (EVSE)”.A “test” or “test sequence” in the singular generally refers to aprocess during which charge, power, or energy is delivered by an EVCScontinuously and without interruption. That is to say, once a deliveryhas been terminated, delivery would not be restarted within the sametest or test sequence. Renewed delivery would be identified as part of asubsequent and separate test or test sequence.

FIG. 1A shows a typical scenario for testing an EVCS. An EVCS 101 istypically an enclosure, which may be free standing or wall mounted. Itusually has at a minimum a display 102, a cable with vehicle attachmentplug 103, and a start charging button 117. Additional controls andindicators may also be present such as an energy pulse output 113. Whendesigned for the purchase of energy by a customer, a credit card orproprietary card/fob reader 114 may also be present. An exemplaryembodiment of the invention is a portable instrument or device 104 whichcontains all the necessary means for performing its functions. It mayuse an internal load, separate programmable load, or an electric vehicle(EV) as load for testing. As shown in FIGS. 1A, 1B, and 2, the device104 may include one or more connection means (e.g., primary port 105,secondary port 106, and control port 115) which are discussed in detailbelow, a display 107 such as a LCD panel for presenting instructions andresults to the user, and a user input device such as keypad 112 forcommunicating with the device. The device 104 may also containcommunication ports such as Ethernet and USB 116. More detail of thedevice's interface to the user is presented below.

According to the exemplary embodiment shown in FIG. 1A, the vehicleattachment plug 103 is inserted directly into the primary port 105 ofdevice 104. Some modern EVCSs may have an energy pulse output 113 fortesting much like an ANSI C12 compliant revenue meter. In this case anenergy pulse pickup 108 of the device 104 may be connected to the energypulse output 113 of the EVCS 101. When the system is used with aprogrammable load 119, then no connection is made to the electricvehicle 111 through charging connector/port 110. The most commonexemplary embodiments have a separate programmable load 119 to makedissipation of the very large heat generated by the load simpler andmake the construction of device 104 more uniform for all embodiments.The programmable load 119 is connected to the main device 104 using acable 120 which connects to the main device 104 just like an EV and acable 118 which allows the main device 104 to control the programmableload 119. Cable 120 connects to the programmable load 119 atconnector/port 124. Cable 118 connects to the programmable load 119 atconnector/port 125.

FIG. 1B shows a slightly different configuration for the programmableload 119 in which the programmable load 119 is divided into two distinctelements: a programmable load controller (PLC) 122 and a fixed load 121.The fixed load 121 is connected to the PLC 122 at connector 123. Thismulti-element configuration allows the actual physical load of the wholesystem to be a fixed load such as a high wattage heater or resistorbank. Such loads generate a tremendous amount of heat when operating atthe top end of the power range which can extend up to 20 kilowatts forAC Level 2 and 100 kilowatts for DC Level 2. Use of an industrial spaceheater is a very cost effective solution for a load. The programmableload controller 122 allows the fixed load 121 to appear to the EVSE asany load from less than one amp to the maximum power capability of theload.

FIG. 2 shows a different connection scenario for a device 104. In FIG.2, the EVCS 101 is connected to the device 104 just as in FIG. 1A. Thatis to say, EVCS 101 is connected to device 104 using a cable with avehicle attachment plug/connector 103 inserted into primary port 105 ofdevice 104. However, instead of the device 104 being connected to aprogrammable load 119 which emulates an electric vehicle from acommunications prospective, an electric vehicle 111 is connected to thesecondary port 106 of the device 104 via a cable 109. In thisconfiguration, the device 104 is in series with the EVCS 101 andelectric vehicle 111, but the electric vehicle charging proceeds asthough the device 104 were not in series. The device 104 may make all ofits measurements during the normal charging operation of the vehicle111. This scenario allows functionality and energy to be measured underreal vehicle load which may have significantly different loadcharacteristics than the standard load presented by the load built intothe device 104 or the programmable load 119.

FIG. 3 provides a block diagram of an exemplary embodiment of theinvention. The EVCS 101 typically has a captive cable terminated by aconnector 103 which plugs into the vehicle 111 through port 110. Mostcurrent electric vehicles in the U.S. use the SAE J1772-201010 standardconnector. To test an EVCS with a device 104 according to the invention,the plug 103 from the EVCS may be connected to a mating socket 309 ofthe primary port 105 of the device 104. The mating socket 309 may be adedicated part of the device 104, or for compatibility with other olderor newer evolving standards may include a connector module 310 andinterface circuits module 311 which allow the entire primary port 105 tobe easily swapped out to accommodate different vehicle connectors andstandards.

Independent of the details of the particular connector 103 or primaryport 105, at least some exemplary embodiments include some or all of thefollowing components:

-   -   (1) Two or more heavy gauge wires carrying the power to the        vehicle (in FIG. 3, these are labeled AC/DC Line 1 308 and AC/DC        Line 2 307). In the J1772-201010 connector, there are two wires        carrying AC power. In the J1772 combo connector under        development as of the filing of this application, there are four        wires: the original two wires of the J1772-201010 standard        capable of supplying AC or DC power, and two additional wires        for DC power capable of much higher voltages and current.        However, in a specific instance only one pair of wires AC/DC or        DC is generally functional at any time;    -   (2) A ground wire for safety purposes;    -   (3) A communications channel for proximity detection which is        capable of communicating with the vehicle 111 to disable its        ability to move while the ECVS 101 is connected. The J1772        protocol uses a single wire with a simple voltage divider to        communicate three states: (a) not connected, (b) button pressed,        and (c) connected;    -   (4) A communications channel for transmission of status and        required power levels between the EVCS 101 and the vehicle 111.        In the present J1772-201010 implementation, a dedicated control        pilot line provides communication between the EVCS 101 and the        vehicle 111. In future versions of J1772, the control pilot        connection may be replaced by an internet protocol communication        scheme such as HomePlug Green Phy over the control pilot or        power line communication (PLC) or other capable communications        technologies.

The inclusion of a connector module 310 and interface circuits module311 provides one approach to dealing with future standards andprotocols. Alternately, specific embodiments with the same functions butdifferent details may be implemented to address as yet unknownconnection and protocol details.

The currents flowing in wires 307 and 308 are detected by measuringdevices/transducer means 312 and 313, respectively, which in someexemplary embodiments may be any one of the following:

-   -   (1) a current transformer (CT). Current transformers are widely        used in electricity meters and high accuracy field test sets.        They provide the advantage of high accuracy (better than 50 ppm)        and full electrical isolation from the power carrying wire. They        are also very temperature stable (better than 20 ppm/° C.).        Current transformers are not applicable for DC currents.    -   (2) a Hall effect sensor/transducer. Hall effect transducers are        generally less accurate (typically 1.0%) than current        transformers and have much worse temperature coefficients (500        ppm/° C.). However, they do provide good electrical isolation        and work for either AC or DC currents. Rapid advances in closed        loop Hall effect technologies may make this a more viable AC/DC        alternative in the near future.    -   (3) a resistive current shunt. Resistive shunts can provide good        accuracy (100 ppm or better) and operate with AC or DC currents.        However they do not provide any electrical isolation and have        significant temperature coefficients. This means that whatever        the charging voltage, it appears at the input of the signal        conditioning circuits 316 and 318 which increases the complexity        of the system;    -   (4) a zero flux transformer. A zero flux transformer is a        special type of active feedback transformer that works for both        AC and DC measurements. It can be accurate (better than 0.03%)        and has a very good temperature coefficient (less than 5 ppm/°        C.). Its disadvantage is one of physical size and cost. A zero        flux transformer may be ten times the size of a similarly rated        current transformer and more than ten times the cost.    -   (5) an AC/DC transducer.

Some embodiments may include only one of the two transducers 312 and 313since that is all that is required by Blondel's Theorem to accomplishthe power measurement task. The two signal conditioning circuits 316 and318 transform the signals from the transducer means 312 and 313 to theappropriate levels needed by each analog to digital converter (ADC) 317and 319 for optimal performance. The signal conditioning circuits mayinclude programmable gain amplifiers controlled by the digitalprocessing means 326. The analog to digital converters 317 and 319convert the analog signals from the signal conditioning circuits 316 and318 to digital form and transmit the information to the digitalprocessing means 326.

One embodiment of the signal processing chain for current measurement isshown in FIG. 4A. Here the transducer is a current transformer 312 or313. The output of the current transformer 312 or 313 is significantlyless than the current flowing in wire 308 (i.e., Line 1), e.g., acurrent 1/1000^(th) of the current flowing in Line 1. This current isconverted into a voltage signal. This may be accomplished by, forexample, passing the current through the two 1.5 ohm resistors. As anexample, an 80 amp rms current in Line 1 is reduced by the examplecircuit shown in FIG. 4A to a 0.240 volt tins signal. The signalprocessing means may include or consist of a differential inputamplifier 402 and a level shifting differential output amplifier 403.According to the present example, amplifier 402 may change the signallevel from 0.240 volts rms to approximately 10 volts peak-to-peak.Amplifier 403 may then convert this 10V signal to a 5 volt peak-to-peaksignal with an offset appropriate for the ADC 405. A voltage reference404 provides a precise stable voltage as reference to the ADC 405 andamplifier network. Power supplies and filter capacitors are not shownfor simplicity but would generally be included. A preferred ADC for allfour instances in this system (that is, ADCs 317, 319, 321, and 323shown in FIG. 3) is a high resolution (e.g., 24 bit), over-sampled SARconverter similar to an Analog Devices AD7766-2. Important parametersare gain and offset accuracy and stability, an internal digital filterthat provides a sharp frequency cutoff, a very large dynamic range, anda very high signal to noise ratio.

To measure the energy delivered both the current and the voltage must bemeasured simultaneously. One or more transducers such as resistivevoltage dividers may be provided to measure voltage on the supply lines.The measuring devices/transducers 324 and 325 which measure voltage fromlines 308 and 307, respectively, are generally resistive voltagedividers. FIG. 3 shows a configuration with two voltage dividers (namelytransducers 324 and 325) although other equivalent configurations mayalso be used in alternative embodiments. The voltage dividers preciselyreduce the voltages of the supply lines from a high level (typically 120to 500 V) to a low level (typically 1 to 10 V) that can be processed bythe signal conditioning circuits 320 and 322. The signal conditioningcircuits may include programmable gain amplifiers controlled by thedigital processing means 326. The analog to digital converters 321 and323 convert the analog signals from the signal conditioning circuits 320and 322, respectively, to digital form and transmit the information tothe digital processing means 326.

Measurement of the current flowing in conductors 307 and 308 alwaysrequires isolation from the voltages on the same lines. This may beaccomplished through the use of an inherently isolated sensor like a CT,hall device, or zero flux transformer, or through special isolated frontend circuitry.

One alternative embodiment of the signal processing chain for voltagemeasurements is shown in FIG. 4B. Here the transducer is a resistivevoltage divider 324 and 325 which reduces the signal voltage from thesupply lines 308 and 307 by several orders of magnitude. In theillustrative example shown, the output of the voltage divider is avoltage 24.9/1024.90=0.0242950 times the input voltage difference ofLine 1 and Line 2. For a 240 volt rms difference the output voltage is5.8308 volts rms. The signal processing means may include or consist ofa unity gain differential input amplifier 407 and a level shiftingdifferential output amplifier 408. Amplifier 407 acts as a very highimpedance buffer. A gain of other than unity may be required to matchthe input requirements of the ADC. Amplifier 408 converts this signal toa 5 volt peak-to-peak signal with an offset appropriate for the ADC 410.The voltage reference 409 may be included to provide a precise stablevoltage as reference to the ADC 410 and amplifier network. Powersupplies and filter capacitors are not shown for simplicity but wouldgenerally be included.

The digital processing means (DPM) 326 generally contains at leastprogrammable logic, a microprocessor core, flash memory, and RAM memory.In this particular embodiment it also contains several low resolutionADCs 351. Depending on the specific chip chosen for any givenembodiment, more of the operations may be executed in firmware asopposed to programmable logic. It will be apparent to those of skill inthe art in view of the teachings herein whether to embody particularoperations discussed herein in programmable logic versus firmware. TheDPM 326 provides control information to many of the interfaces in thedevice 104. It may also provide timing and collect multiple streams ofdata. If the EVCS 101 is equipped with an energy pulse output 113 thenthe energy pulse pickup 108 may be connected to the EVCS 101 so thedevice 104 can automatically track how much energy has been deliveredaccording to the EVCS 101.

FIG. 5 shows a block diagram of the functionality of the digitalprocessing means (DPM) 326 according to an exemplary embodiment. Thiscan be implemented in, for example, a field-programmable gate array(FPGA) such as a Xilinx 7-Series FPGA with embedded processor or bycombining a smaller FPGA such a 6-Series with a dedicated processor suchas a Freescale iMx series processor. In all implementations, the centralprocessing unit 501, serial peripheral interface (SPI bus), controllerarea network (CAN bus), and ethernet interfaces used for adapter control502, keyboard interface 503, video interface 504, power control 505, USBinterfaces 510, Ethernet interface 509 (if desired in addition toadapter control 502 or secondary adapter interface 508), and secondaryadapter interface 508 may all be standard interfaces on embeddedprocessors. The firmware to support these interfaces is generally partof all modern embedded operating systems. Most modern chips appropriateto implement the DPM 326 contain large RAM memories 506 and FLASHmemories 507 sufficient for this application. Should either internalmemory prove insufficient in size, additional external memory chips (notshown) may easily be added.

The data acquisition and control logic 511 is important to theperformance of the system. As one important function, it establishes thedata sampling sequence. A master clock of 19.6608 MHz (or some othersuitable frequency) is provided by, for example, a crystal oscillator.The 19.6608 MHz is a particularly useful frequency for power measurementapplications because it is a multiple of both 50 Hz and 60 Hz. Thetiming logic may use this base frequency for all operations in thedigital processing. From the master clock the two clocks required by theADC are generated. An exemplary MCLK frequency is 983,040 Hz which isthe master clock divided by 20. For the illustrative exampleconfiguration shown, SCLK is equal to MCLK. This provides a sample datarate from each ADC of 30,720 Hz. This provides precisely 512 samples percycle of the 60 Hz waveform. This provides very high sampling forexcellent accuracy. Sampling at lower rates of, for example, 256, 128and 64 samples per cycle also generally provide acceptable performance.Sampling at higher rates (e.g., 1024 or 2048 samples per cycle) could beused, but may provide little additional benefit.

According to an exemplary embodiment, to start the acquisition process,SYNC is asserted for a minimum of 5 MCLK cycles. After a delay of 2370MCLKs the ADCs will assert DRDY which is used to gate data into theserial to parallel conversion registers 514. When DRDY is deasserted,then a DMA transfer to processor memory is initiated. Included in thedata transferred is a time stamp originating from a timer register 512which increments at the master clock rate and a flag register 513 whichcontains a bit indicating a zero crossing and a bit indicating an energypulse. This time stamped data stream is suited to provide all necessaryinformation for the computation of energy detailed below. Once dataacquisition is started it will continue at the sample frequency untilthe digital processing means 326 terminates it.

Today the measurement of power quantities is done almost exclusivelywith the employment of digital sampling based algorithms. When one has astream of data based on constant frequency sampling, one can select aset of definitions for Active Power, Apparent Power, and Reactive Powerwhich are easily implemented in modern processors and deliver resultswhich match those expected by a careful engineering analysis.

One of the principal functions of exemplary embodiments of the inventionis the accurate calculation of energy. More specifically, the digitalprocessing means 326 is configured to calculate a value of active energydelivered by the EVCS to the load 119. The instrument hardware, inparticular one or more measuring devices or transducers 312 and 313,produces a stream of simultaneous or substantially simultaneousmeasurements of voltage and current. For embodiments with a pair ofsupply lines, the current measured on Line 1 (wire 308) and Line 2 (wire307) should be precisely equal but opposite in sign. Only one of the twopossible measurements is needed for the calculations. From the voltagesmeasured on Line 1 and Line 2 relative to ground, we compute the voltagedifference between the two lines. Given that I_(n) is the currentmeasured at an instant in time in Line 1 and V_(n) is the voltagebetween Line 1 and Line 2, then the various forms of energy can becomputed with the measurements I_(n) and V_(n) using the standardformulations for active, reactive, and apparent energy in both timedomain and frequency domain for AC based systems. For DC based systemsonly the time domain approach is valid.

Measurements made directly in the time domain have the advantage thatthey are very simple to implement and provide definitive answers underall conditions. There is no assumption of a repetitive waveform andsudden changes in amplitude are readily handled correctly. There are twoimplementational complexities in a fixed sampling frequency approach:(1) In the equations defined below, the simplest approach includes anyDC component in the signal. However the effect of the DC component canbe removed if it is significant. (2) If the frequency of the measuredsignal is not an exact multiple of the sampling frequency, then caremust be taken to measure the actual frequency, use appropriatefractional points at the start and end of the integration, and performnormalization correctly.

Time Domain Calculations$V_{rms} = \sqrt{\frac{1}{N}{\sum\limits_{n}\; V_{n}^{2}}}$ RMS Voltage(V) $I_{rms} = \sqrt{\frac{1}{N}{\sum\limits_{n}\; I_{n}^{2}}}$ RMSCurrent (I) $P_{t} = {\frac{1}{N}{\sum\limits_{n}{V_{i}I_{i}}}}$ ActivePower (P_(t)) - Calculation includes any DC component as well as allfrequencies in the signal up to the Nyquist frequency.$S_{t} = {{VA} = {{{V\;}_{rms}I_{rms}}\; = \sqrt{\frac{1}{N}{\sum\limits_{i = 0}^{i = {N - 1}}\;{{V_{i}^{2} \cdot \frac{1}{N}}{\sum\limits_{i = 0}^{i = {N - 1}}\; I_{i}^{2}}}}}}}$Apparent Power (S_(t)) - Calculation includes any DC component as wellas all frequencies in the signal up to the Nyquist frequency. Q_(t) ={square root over (S² − P²)} Reactive Power (Q_(t)) - There is not agood formulation in the time domain for directly computing Q. Thisexample adopts the approach of computing it from the “Power Triangle”assumption.

All summations must account for the exact number of samples in a cycleincluding fractional data points and properly normalize for the lengthof the cycle when doing multiple cycle summations to calculate energyrelated quantities. The above are a consistent set of definitions forall of the energy quantities and are the preferred implementation forthe system. However, the definitions above are not intended to restrictthe system from using alternative definitions based on the sampledvoltages and currents if appropriate.

An alternative approach to using the sampling data directly in the timedomain is to use the sampling data to do a Fourier analysis on thewaveforms. One of the basic assumptions of Fourier analysis is that thewaveform is repetitive over the interval of analysis. While real worldwaveforms are not perfectly repetitive over long periods of time, theassumption of repetitiveness over a small number of cycles is usuallyquite good.

According to Fourier's Theorem any periodic signal can be represented inthe following manner:

${V(t)} = {\frac{a_{0}}{2} + {\sum\limits_{n = 1}^{\infty}( {{a_{n}{{Cos}( {n\;{\omega\;}_{0}t} )}} + {b_{n}{{Sin}( {n\;\omega_{0}t} )}}} )}}$

Frequency Domain Calculations$V_{rms} = {\frac{1}{\sqrt{2}}\lbrack {\sum\limits_{n}\;( {a_{vn}^{2} + b_{vn}^{2}} )} \rbrack}^{1/2}$RMS Voltage⁽¹⁾⁽²⁾$I_{rms} = {\frac{1}{\sqrt{2}}\lbrack {\sum\limits_{n}\;( {a_{in}^{2} + b_{in}^{2}} )} \rbrack}^{1/2}$RMS Current⁽¹⁾⁽²⁾$V_{1} = {\frac{1}{\sqrt{2}}\lbrack {a_{v\; 1}^{2} + b_{v\; 1}^{2}} \rbrack}^{1/2}$RMS Voltage - Fundamental Only⁽¹⁾$I_{1} = {\frac{1}{\sqrt{2}}\lbrack {a_{i\; 1}^{2} + b_{i\; 1}^{2}} \rbrack}^{1/2}$RMS Current - Fundamental Only⁽¹⁾ $\begin{matrix}{P_{f} = {{\sum\limits_{n}\;{{{\overset{\_}{V}}_{n} \cdot {\overset{\_}{I}}_{n}}}} = {{\frac{1}{2}{\sum\limits_{n}\;( {{a_{vn}a_{in}} + {b_{in}b_{vn}}} )}} =}}} \\{\sum\limits_{n}\;{V_{n}I_{n}\mspace{11mu}{\cos( \theta_{n} )}}}\end{matrix}\quad$ Active Power (P_(f)) - Active power computed bysumming the vector dot products for each of the harmonics⁽¹⁾⁽²⁾$P_{1} = {{{{\overset{\_}{V}}_{1} \cdot {\overset{\_}{I}}_{1}}} = {{\frac{1}{2}\lbrack {{a_{v\; 1}a_{i\; 1}} + {b_{v\; 1}b_{i\; 1}}} \rbrack} = {V_{1}I_{1}\mspace{11mu}{\cos( \theta_{1} )}}}}$Active Power (P₁) - Active power for the fundamental frequencyonly.⁽¹⁾⁽²⁾$S_{f} = {\frac{1}{2}\lbrack {\sum\limits_{n}\;{( {a_{vn}^{2} + b_{vn}^{2}} ){\sum\limits_{n}\;( {a_{in}^{2} + b_{in}^{2}} )}}} \rbrack}^{1/2}$Apparent Power (S_(f)) - Apparent power computed by summing the Vrmstimes Irms for each harmonic.⁽¹⁾⁽²⁾$S_{1} = {\frac{1}{2}( {a_{v\; 1}^{2} + b_{v\; 1}^{2}} )^{1/2}( {a_{i\; 1}^{2} + b_{i\; 1}^{2}} )^{1/2}}$Apparent Power (S₁)—Apparent power computed as Irms times Vrms for thefundamental only.⁽¹⁾ $\begin{matrix}{Q_{f} = {{\sum\limits_{n}\;{{{\overset{\_}{V}}_{n} \times {\overset{\_}{I}}_{n}}}} = {{\frac{1}{2}{\sum\limits_{n}\;( {{a_{vn}b_{in}} - {a_{in}b_{vn}}} )}} =}}} \\{\sum\limits_{n}\;{V_{n}I_{n}\mspace{11mu}{\sin( \theta_{n} )}}}\end{matrix}\quad$ Reactive Power (Q_(f)) - Reactive power computed bysumming the vector dot products of each of the harmonics⁽¹⁾$Q_{1} = {{{{\overset{\_}{V}}_{1} \times {\overset{\_}{I}}_{1}}} = {{\frac{1}{2}( {{a_{v\; 1}b_{i\; 1}} - {a_{i\; 1}b_{v\; 1}}} )} = {V_{1}I_{1}\mspace{11mu}{\sin( \theta_{1} )}}}}$Reactive Power (Q₁) - Reactive power for the fundamental only⁽¹⁾ Notes:⁽¹⁾The a₀ component is generally not included but could be if desired.⁽²⁾If N is sufficiently large so all frequencies in the signal areincluded and the signal is periodic, then this equation will give theexact same value as the same quantity measured in the time domain.

The above frequency domain formulations for Watts and volt-amps (VA)generate numeric results for all periodic waveforms that are the same asthose in the time domain. The formulation of the volt-ampere reactive(VAR) calculation takes the single frequency definition of VAR andextends it to the full Fourier spectrum.Q=VI sin(θ)

For proper application of the above formula the computations should bedone over a few cycles at a time for AC signals and then the results ofthese short interval power calculations are summed over the entiremeasurement period to produce the relevant energy results. This isespecially important when using the Fourier computations undercircumstances where the waveforms are varying with time.

In the case of TOTAL test modes described below, the calculationsdescribed above can start as soon as voltage is detected on Line 1 andLine 2. All answers will be zero until current begins to flow. Thecalculations end after the current has ceased to flow, at which pointthe VI product is again zero. Said differently, for a device 104 givinga value of active energy delivered from an EVCS 101 to a load 119, thevalue of active energy delivered may be calculated by a digitalprocessing means 326 from a continuous stream of sampling measurementsmade over an entire time period from a first sampling measurement to afinal sampling measurement, where the first sampling measurement startsat or before a start of power transfer through the primary port 105 andthe final sampling measurement is made at or after an end of powertransfer through the primary port 105.

When the energy pulse mode is being used, a separate set of calculationsmay be performed in parallel that begins synchronously with an energypulse and runs for a precise and typically predetermined number ofpulses. Each pulse from the EVCS represents a precise amount of energy,for example: If the EVCS emits a pulse every 1.8 W-Hrs and we measurefor 100 pulses, we would expect to measure 1.8×100=180 W-Hrs of energyin the device 104.

The digital processing means 326 may also provide support forinterfacing with the user through one or more output devices (e.g., adisplay 107) and one or more user input devices, for example key pad112. Output and input devices may be one in the same, such as displays107 which are touchscreens. In some embodiments, measurements may bestored in the memory of the digital processing means 326. Output devicesmay include one or more displays 107 and/or communication links orinterfaces to external devices such as but not limited to externalmemory devices, laptops, tablet computers, smartphones, or otherdevices. Communication with external devices, transfer of data, remotecontrol and other features may be facilitated by one or more standardinterfaces such as USB 342 and Ethernet 341. The one or more outputdevices are usable to display or transmit the value of active energydelivered as calculated by the DPM 326 and/or display or transmit one ormore values pertaining to the value of active energy delivered (e.g., adifference, percentage error, etc. calculated from the first value ofactive energy delivered).

After the value of active energy delivered has been determined, it canthen be compared with a metered value of active energy delivered givenby the EVCS 101 on, for example, a display 102 thereof. In someexemplary embodiments, the digital processing means 326 may beconfigured to perform this comparison. The device 104 may obtain themetered value of active energy delivered as output by the EVCS by, forexample, the user reading the metered value from the EVCS and manuallyentering it via an input device such as keypad 112. The one or moreoutput devices of the device 104 may then display or transmit to anexternal device a result of the comparison. The result of the comparisonmay take a variety of forms. As one example, the result of thecomparison may be an indication of whether or not a difference betweenthe value of active energy delivered calculated by the DPM 326 and themetered value of active energy delivered as given the EVCS exceeds somepredetermined threshold. Such an error threshold may be set by themanufacturer or by the user and be based on company or industrystandards on acceptable error or deviation of an EVCS's internalmetering. As another example, the result of the comparison may indicatea magnitude by which the value of active energy delivered calculated bythe DPM 326 and the metered value of active energy as given the EVCSdiffer from one another. A user may in this case then compare thisdifference to acceptable deviations per a company or industry standard.

The final part of the circuitry required are the several interfacesbetween the EVCS and the electric vehicle that control the chargingprocess. SAE J1772-201010 is currently the dominant standard forcharging in the United States, though it is under revision and expectedto change again in the near future. FIG. 3 shows the two communicationslines PROXIMITY detect 328 and CONTROL PILOT 327 that are part of theSAE J1772-201010 standard. The signaling sequence for the SAEJ1772-201010 standard is well documented in the standard and manywebsites. Only a brief description is provided here for completeness.Also shown is the interface control signal(s) 329 which allow amulti-protocol interface module 311 to be controlled by the DPM 326.

FIG. 6 shows example circuitry for an exemplary embodiment which meetsthe requirements set by SAE J1772-201010. For convenience, themonitoring circuitry for the PROXIMITY detect 328 and CONTROL PILOT 327signals may be located in the device 104 while the circuitry thatresponds to the EVCS may be located in the programmable load 119. Thisallows the device 104 to be the same in all testing modes: that is,whether the load is provided by a programmable load 119 (an “active”test mode) or an EV 111 (a “passive” test mode). When connector 124 isconnected resistors R4 and R5 provide the appropriate voltage level tothe Proximity Signal. If S6 and S5 are both open then the EVSE will notdetect the load as being connected. Closing S6 signals to the EVSE thatthe load (EV) is connected but not ready to charge. Closing S5 signalsto the EVSE that the load (EV) is ready to receive a charge. S3 is usedto short out the diode D1 which results in a fault condition beingdetected by the EVSE, leading to an immediately shut down.

An example sequence of events and signals occurring during connectionand removal of the connector 103 to an EV is shown in FIG. 7. Becauseprogrammable load 119 emulates an EV, for some of the elements (e.g.,resistors and switches) of the programmable load 119 shown in FIG. 6,the same or equivalent elements exist in an EV. As such, in describingFIG. 7 herein, reference may be made to components shown withinprogrammable load 119 in FIG. 6, and it is to be understood that theseelements or their equivalents are also found in an EV. At 701, theconnector 103 has not been connected to the EV 111. The proximity signal605 is at 4.5 V and the PILOT CONTROL (PC) 604 is at 0 V. At 702,connection of the connector 103 causes the voltage at 605 to drop to 1.5V. This signifies to the electric vehicle that it is connected to aEVCS. This may happen immediately (if resistor R6 is connected to groundvia S6) or under control of the digital processing means 326 bycontrolling S6, depending on the details of the test scenario. At 703,once the connector 103 is plugged into port 105 and S6 closed, the PCvoltage drops to 9 V, signaling the EVCS to start sending its PWM signalthat signifies maximum available charging current at 704. At 705, the EVadjusts its current draw to match the EVCS capabilities. The EV signalsthat it is charging by connecting R7 to ground. This drops the positivepeak voltage of the PWM signal to 6V. The EV continues to charge untilthe battery is fully charged at 706, the user depresses a button onconnector 103 to stop charging. If charging completes, then at 707, theproximity signal rises to 2.75 V which signals the EV to stop chargingand remove its load. The EV returns the peak PC level to 9V. At 708, theECVS removes power from the cable, at which point is safe for the userto disconnect the connector 103 from the EV.

The proximity signal may have three voltage levels as seen by anelectric vehicle 111 or the device 104: (1) when no connection is madethe voltage is at a maximum (e.g., 4.5 VDC), (2) when the connector 103is connected to the EV 111 or device 104 the voltage drops to a minimum(e.g., 1.5 VDC), and (3) if the button on a SAE J1772 handle is pressedthe voltage rises back up to a mid level between the maximum and minimum(e.g., 3.0 VDC). Dropping the voltage to the minimum (e.g., 1.5 VDC)signals the EV 111 or device 104 that an EVCS 101 is connected andstarts the charging sequence. Pressing the handle button signals theECVS 101 that the user wishes to disconnect the charging cable. In theillustrative example shown in FIG. 6, the resistor network with a 330ohm resistor and 2.7 k ohm resistor together with the buffer amplifier601 correspond with signal conditioning circuitry 338 in FIG. 3 andproximity interface 516 in FIG. 5.

In continuance of the same illustrative example introduced with respectto FIG. 6, the control pilot (CP) signal is 12 VDC at the J1772 plugbefore it is connected. When connected the level is pulled down to 9 VDCby R6 in the device 104. This is detected by the EVCS 101 and the 12 VDCsignal is switched by S1 to a +12V to −12V pulse width modulated signal.The frequency is 1000 Hz. The current delivery capability of the EVCS101 is encoded in the width of the positive portion of the CP signal. A10% duty cycle signifies 6 A. A 96% duty cycle signifies 80 A. Dutycycles for intermediate levels are specified by the J1772 documentation.When the EV 111 or device 104 detects the PWM signal, it increases theload (e.g., by switching S5 to add R7 in parallel to R6 switched by S6)on the signal, dropping the peak positive voltage to 6V and beginning todraw current not to exceed the maximum signaled by the EVCS 101. Whencharging is complete the EV 111 or programmable load 119 signalstermination of charging by allowing CP to return to 9V peak (R7 isswitched out of the circuit). The signal conditioning 339 in FIG. 3 andpilot interface 517 in FIG. 5 is shown in more detail in FIG. 6. Abuffer amplifier 602 delivers the CP signal to one of the ADCs 351 thatare part of the digital processing means 326. This signal may bedigitized at a rate of 100K samples per second or higher. This allowsamplitudes, frequency, and pulse width to be monitored.

A device 104 may derive AC power from one or multiple sources. Twoexemplary sources are: (1) from the power delivered by the EVCS or (2)from power delivered to the AUX AC power connector 332. A switch 331 maybe provided which allows AC power to be directed to the system powermodule 337 from either the EVCS connection at the primary port 105 orthe auxiliary power connection at 332. The system power module 337converts the AC power to the levels needed by the internal circuitry andmay control charging of a battery 333 which serves as a further sourceof power for the device 104. If auxiliary AC power or EVCS power isavailable, the system may operate off of that source. If no externalpower is available, the device 104 may operate off of its internalbattery 333. The internal battery 333 may automatically charge if neededwhen external power is available. The system is capable of operating fornormal testing periods exclusively from the battery 333 if needed.

In some exemplary embodiments, a facility such as a ground fault testcircuit 306 allows the functionality of the EVCS's ground faultprotection circuitry to be tested by applying a known leakage betweeneither of the two power conducting lines 308 and 307 and ground. Thistest is generally performed outside of the energy measurement processsince it should cause an immediate stoppage in the EVCS providingvoltage and current to the load.

In some exemplary embodiments, another test function of shorting outdiode D1 may be implemented. When the diode is shorted the amplitude ofthe negative pulse height drops to match the positive pulse height. Thisis considered an error by the J1772-201010 protocol and should result inimmediate removal of the charging voltage and current.

Though the programmable load 119 is conceptually very simple, e.g. a setof appropriately sized resistors switched in and out by relays orelectronically with triacs, care must be taken in the design, especiallyat higher currents. For 120 volt EVCSs (Level 1), loads of 120 watts(1.0 A), 750 watts (6.3 A), 1500 watts (12.6 A), and 1850 watts (15.4 A)can be constructed using heating strips or power resistors with forcedair cooling. For 240V systems, loads of 120 watts (0.5 A), 1700 watts(7.0 A), 3400 watts (14.0 A), and 7200 watts (30.0 A) can also beconstructed from heating strips or power resistors. Based on the currentstate of standards development, this loading selection is expected toallow all systems of AC Level 1 and 2 and DC Level 1 to be tested. Otherload conditions for testing starting current (a very low load) caneasily be added to the available load values if required. Loads withmuch higher current capacity may also be connected, but that is notexpected to be required. Industrial style portable heaters can also beeffectively used as loads with appropriate controllers to allow loadcontrol. Using an electric vehicle 111 as the load always has theadvantage of making use of the energy for the test rather than wastingit.

To meet the testing needs for current and future requirements in theface of rapidly evolving standards, a more flexible approach may bepreferred compared to the simple switched resistive load approachdescribed above. The preferred approach should allow for any load fromless than one amp to the full capacity of the EVSE to be presented ondemand. Testing requirements of NIST Handbook 44 are expected to requiretesting at less than 10% of available load and at >85% of availableload. Since the available load is not known until the EVSE presents thePWM signal on the control pilot signal 517, using switchable fixed loadsis difficult to implement in practice because many different resistancevalues must be switched in and out. To solve this problem, aprogrammable load controller 122 (see FIG. 1B) is provided which uses achopper type technology to make a fixed load appear to the EVSE as anyload desired. By applying appropriate filtering in the design, a lowdistortion sinusoidal or DC load wave form is maintained. Use of pulsewidth modulated control allows us to achieve an effective load which canbe smoothly varied (e.g., in steps of less than 0.1 percent) from lessthan 1 percent of full load to 100 percent load.

FIG. 9 shows the details of the programmable load controller (PLC) 122(see FIG. 1B). This controller fully emulates the operation of anelectric vehicle. From the point of the EVSE it looks exactly like acar. The advantage is that by monitoring the Control Pilot signal 517and communicating with the primary device 104 the load can set theeffective load seen by the EVSE to any value consistent with the maximumload capability as presented by the EVSE. The PLC 122 contains aprocessing means 610 (e.g., a microcontroller) with a modifiable storedprogram for controlling the function of the device. The communicationsto the EVSE is provided by interfaces 516 and 517. Communication to theprimary device 104 is provided by a standardized interface, such asRS485, through connector 125. Power for the control logic is providedthrough this connector. The load current controller 901 includes achopper circuit 1002 (see FIG. 10) that through pulse width modulationallows the load current to be controlled from a small quiescent level,e.g. less than 0.5 amps, to the full capacity of the one or moreattached fixed load(s) 904 which are external. Because the J1772standard allows only a very small leakage current from L1 or L2 toground, the isolated gate driver 902 for the load current controller 901must provide isolation from the ground of the control electronics.Because of the large amounts of heat generated, an automatic thermalshutdown sensor circuit 903 has been implemented and ambient temperaturemonitoring via ambient temperature sensor circuit 906 is provided.Connection to the fixed load(s) 121/904 is generally through anappropriately rated standard NEMA connector 123.

FIG. 10 explains the operation of the load current controller 901.Diodes D1001, D1002, D1003, and D1004 create a full wave bridge whereD1001 and D1004 provide a path for the first half of the AC cycle andD1002 and D1003 provide the path for the second half of the cycle. Thisenables the load current controller 901 to fully utilize the whole ACcycle to produce the maximum output current that is needed. In order forthe programmable load 119 to control the current going into the fixedload 904 (e.g., a portable industrial heater or resistor bank), powerswitching transistor Q1001 is driven by a PWM signal where its dutycycle corresponds to the desired fraction of the maximum current thefixed load 904 is capable of drawing. Q1001 is a power switchingtransistor that can be, for example, a MOSFET or an IGBT. An IGBT ispreferred because it provides very fast switching, provides low powerdissipation, and requires low drive voltage and current. R1001 & C1005act as a snubber to filter out high voltage spikes created when currentthrough L1001 suddenly changes due to the switching of Q1001. The lowpass output filter 1003 conditions the signal from the dynamic effectsof the chopping process. By appropriately selecting the frequencyresponse of the filter networks 1001 and 1003 and the snubber (i.e.,combination of R1001 and C1005), the load as seen by the EVSE can havelow distortion and substantially unity power factor. The power transfercapability of the load current controller 901 can be increased to almostany level by appropriate choice of the diodes and power switchingtransistor (e.g., IGBT) Q1001 and/or by adding additional diodes orIGBTs in parallel with those shown in FIG. 10. Power factor is definedas the cosine of the phase angle between the voltage and current waveforms. For unity power factor this angle is zero, i.e., the voltage andcurrent are in phase. The specifications of the present standards forelectric vehicles (SAE J-2894 and IEEE519) require that a car present aload with power factor of at least 0.95 with a total harmonic distortionof no greater than 10 percent. Load current controller 901 meets theserequirements with a wide margin A load current controller 901 accordingto the invention has substantially/near unity power factor, meaning apower factor which is at least greater than 0.95. The load currentcontroller 901 also has total harmonic distortion below 10 percent. Inexemplary embodiments, power factor of the load current controller 901is typically greater than 0.98 and total harmonic distortion less than 5percent.

Power switching transistor Q1001 is controlled by an isolated gatedriver 902. A gate driver is necessary for the design since the inputvoltage needed to drive Q1001 is relatively high and must beelectrically isolated from the rest of the circuitry. Isolation isrequired to prevent the large currents flowing in the emitter circuit ofthe IGBT Q1001 from flowing into the safety ground of the system. Theduty cycle of Q1001 is preferably controllable from less than 0.5percent to 100 percent.

Three of the important requirements for the operation of the loadcurrent controller 901 are a high input voltage to drive IGBT Q1001,fast rise and fall time transitions needed to attain the needed dutycycle of the PWM signal and minimize power dissipation in the IGBTQ1001, and ground isolation, where emitter circuit should be separatedfrom the safety ground. This presents a challenge since the usualapproach of using a pulse transformer to achieve the isolation cannot beused because pulse transformers are generally limited to a maximum dutycycle of approximately 50 percent. While an opto-isolator may be used,this requires a separate isolated power supply.

According to a preferred solution, in order to solve the duty cycleissue, two or more pulse transformers (i.e., pulse transformer circuits)L1003 and L1004 are used. The outputs of the two pulse transformercircuits L1003 and L1004 are ORed as the input to IGBT Q1001. If therequired load current requires a 50% duty cycle or duty cycle less than50% (e.g., ≦49%, ≦48%, ≦47%, ≦46%, ≦45%, ≦40%, ≦30%, ≦20%, ≦10%, ≦5%, or≦1%) only the L1003 transformer is used. For duty cycles higher than 50%(e.g., ≧51%, ≧52%, ≧53%, ≧54%, ≧55%, ≧60%, ≧70%, ≧80%, ≧90%, ≧95%, ≧99%,or 100%), the configuration is such that L1003 will be activated with amax duty cycle of 50% and before L1003 is deactivated, L1004 isactivated providing a small overlap time that will support uninterruptedgate driving. L1004 will be activated based on the remaining duty cyclerelative to the total required. In this way an effective duty cycle of100% can be accomplished with transformer isolation. Resistor R1002 anddiode D1005 and resistor R1003 and diode D1006 provide soft start andfast stop for the IGBT Q1001.

Safety protection for the high power components D1001, D1002, D1003,D1004, and Q1001 is provided through a hardware thermal shutdownmechanism 903 where, when the case temperature of these components goesabove predefined limits, the input to Q1001 is pulled to ground,shutting down the energy transfer.

The device 104 may also include additional interfaces available to theDPM 326 to allow it to perform ancillary tasks. For example, a GPSsubsystem module 350 would allow the system to determine its location.This may be used to access a database of information stored on thedevice to determine the test location, possible EVCS systems at thelocation, and retrieve site specific data to make the test personnel'ssetup and documentation tasks easier. Test results may also be stored inthe database. Wireless communications channels such as ZIGBEE 349, BLUETOOTH 348, and WIFI 347 may also be included as convenience features tothe user to eliminate the need for ancillary equipment at the test site.

FIG. 11 shows the performance of a preferred embodiment of theprogrammable load controller 122. The design requirement is to have theinput current of the programmable load controller (which is the outputcurrent of the EVSE) to be near unity power factor and be sinusoidal innature without high levels of distortion. FIG. 11 shows the inputcurrent of the programmable load controller 122 as the duty cycle isscanned from 5 percent to 95 percent. The desired performance isachieved in that the power factor is never less than 0.98 and there isvery low harmonic distortion. The performance of the controller is notsignificantly affected by the value of the load resistance. The powerfactor remains better than 0.98 from loads of 3 to 60 ohms.

FIG. 12 shows a plot of input current to the programmable load 119 (thatis, the output current from EVSE) versus duty cycle of the choppercircuit 901. Of primary importance is that the current can be smoothlyvaried from near zero to full load. The communications between the maindevice 104 and the programmable load controller 122 allows themeasurements of current made by the main device 104 to be used to allowthe programmable load controller to adjust its duty cycle to giveexactly the desired current load for the EVSE.

Operation

The principal focus of devices and methods herein is the safe and easydetermination of the energy measurement and billing accuracy of an EVCS.In particular, devices and methods according to the invention permitdetermination of active energy delivered to a load. For clarification,instantaneous power is the product of the voltage and current at amoment in time. Active power is “The time average of the instantaneouspower over one period of a wave.” (IEEE 100). Power is essentially arate of flow analogous to gallons per minute for a liquid dispenser. Wemeasure power in terms of kilowatts (kW). Energy is the integral ofpower over a period of time. We measure energy in terms of kilowatthours (kWh). The analogy to a liquid dispenser is gallons. As anillustrative example, an EVCS operating at 120 VAC and delivering acurrent of 20 amps rms is operating at a power level of 2.4 kW. If youcharged an electric vehicle for 8 hours at this power level you wouldhave delivered 19.2 kWh of energy to the vehicle. That is, 19.2 kWh ofactive energy has been delivered by the EVCS to the vehicle. Notably,the prior art does not provide any mechanism which determines the activeenergy delivered by an EVCS to a vehicle or other load.

It should be noted that a determination of energy delivered by an EVCSdiffers greatly from mere communications protocol verification andvalidation. While communications protocol verification and validation isuseful and employed by exemplary embodiments disclosed herein, these arenot the same as a transactional verification whereby an EVCS is testedto determine whether or not the EVCS is accurately reporting the activeenergy (as measured in, for example, kWh) transferred from/through theEVCS to a load (e.g., an electric vehicle or a load emulating anelectric vehicle). In short, communications protocol verification andvalidation alone fail to take into account or consider measuring anamount of energy, particularly active energy, that is delivered in asingle transaction (e.g., a single delivery, analogous to a singlefill-up at a gas station pump).

In Schulz (US 2013/0346010 A1), systems and methods of testing andverifying communications protocols are disclosed, but Schulz fails toprovide consideration or the necessary implements for calculating avalue of active energy delivered by an EVCS to a load. Furthermore,Schulz fails to disclose any form of determining or calculating energymeasurement accuracy. In contrast, exemplary embodiments disclosedherein may provide for or perform a comparison of energy deliveredvalues as displayed or output by an EVCS with energy delivered valuesdetermined by the devices and methods of embodiments of the invention.

One of the use cases for electric vehicles contemplates allowing thevehicle to provide energy to the electric grid from its battery ratherthan receive energy from the grid. While this is not yet a commonpractice, it is a possible mode of operation. The device 104 can beconfigured to measure power flow in either direction: delivered (EVCS tovehicle) or received (vehicle to EVCS). If this operating mode comesinto practice the EVCS's metering functionality will have to be testedfor both directions of energy flow.

Exemplary embodiments of the invention support at least two differentapproaches to the test scenario: active test mode and passive test mode.

Active Test Mode: In active test mode, a load is supplied independent ofan actual electric vehicle 111. A programmable load 119 may either beintegral with or attachable to device 104 to provide the load 119required to test the system. Programmable load 119 may be connected tothe primary device 104 via the secondary port 106 using connector 120.The programmable load 119 may be either a resistive load or a morecomplex electronic load designed to emulate the load presented by anelectric vehicle. In either case, the current drawn by the load may becontrolled by the digital processing means 326 through communication tothe load controller 610 via connector/control port 115, cable 118, andconnector 125. Within this test mode there are three different scenariosfor the accurate measurement of energy flow depending on whether theEVCS is equipped with an energy pulse output 113.

Passive Test Mode: In passive test mode, the EVCS is plugged into theprimary port 105 of the invention and an electric vehicle 111 is pluggedinto the secondary connector 345 of the secondary port 106 using a cable109. In this test mode, all of the signals from the EVCS 101 areeffectively transmitted through the device 104 to the electric vehicle111 being charged. The device 104 may measure all of the signalstransmitted between the EVCS and the EV, verify communications protocolsand accuracy, and measure the energy delivered to the vehicle by theEVCS.

FIGS. 8A, 8B, 8C, and 8D show individual flow diagrams for each of fourtest modes with exemplary operational sequences.

Active Mode, Total Energy Test (“TOTAL”)

FIG. 8A is a flow diagram for an active mode, total energy test(“TOTAL”). No energy pulse may be available. In this test mode thedevice 104 measures all energy flows from the EVCS 101 from the time theEVCS 101 is connected to device 104 until the EVCS 101 is disconnected.This is preferably the default mode of the system.

The process begins at start 801. The user then sets up this mode byinteracting with the software through the keypad 112 and display 107.Exemplary setup information entered at 802 is as follows:

-   -   Select ACTIVE Mode (Device 104 serves as the load for the EVCS        101 or, alternatively, a standalone programmable load 119 is        connected to the secondary port 106 of the device 104.)    -   Select TOTAL Energy Measurement (All energy delivered by the        EVCS 101 is totaled.)    -   Enter Charging Time (A time to run the test is selected/entered.        In this operational sequence, the energy measurement generated        by device 104 may be manually compared to the display on the        EVCS 101. Alternatively, the data from the EVCS display may be        input to the device 104, after which the device 104 (e.g., with        DPM 326) computes the accuracy of the EVCS-generated values by a        comparison with the values generated by the device 104 itself.        The device 104 may also verify the billing computation in        addition to the accuracy of the total energy delivered values.        In this case, it is advantageous to run the test for a        sufficient duration of time to ensure that the resolution of the        display of the EVCS 101 does not significantly limit the        measurement's accuracy.)    -   Set Charging Current (The programmable load 119 is enabled by        the user selecting the charging current for the test.) As an        alternative to the user manually setting a load, the device 104        may operate in an automatic mode (“AUTO”) where it selects the        load to be applied based on the output capability of the EVCS as        encoded in the pilot control signal. Multiple test sequences can        also be setup to allow for testing at a high load (>85% of        maximum) and at low load (<10%) of maximum automatically.    -   Test GFCI (ground fault circuit interrupter) (yes or no)    -   Test pilot control diode (yes or no)

Because this sequence is a TOTAL energy measurement test, energymeasurement starts immediately at 804. The user is instructed at 805 toinsert the EVCS plug into the primary port 105 of the device 104. Oninsertion, the device 104 signals the appropriate levels on thePROXIMITY line at 806 and awaits the CONTROL PILOT protocol as discussedearlier in reference to FIG. 6. For some embodiments, the user may haveto interact with controls on the EVCS to initiate the CONTROL PILOTexchange. The device 104 verifies the PROXIMITY at 807 and generates astart charging state on the CONTROL PILOT 809. If the exchanges weresuccessful, the EVCS 101 will start delivering power; if not, an errorwill be reported at 810. If in AUTO load mode, the device 104 adjuststhe load 812 if necessary to meet requirements of the applicablestandard such as J1772-201010. When the load has been set manually itverifies that the load does not exceed the capability of the EVCS. Itthen verifies that all charging parameters (e.g., current, voltage,ripple, slew rates, etc.) are within J1772-201010 or other appropriatestandard's specifications at 813. If one or more parameters are notwithin specification, an error is reported at 814, charging isterminated, and the test terminated. If all parameters are withinexpected ranges, then the test will continue for the preset time at 815.Once the test is completed (e.g. the preset time duration for the testhas elapsed as determined by the digital processing means 326), thedevice 104 will signal via the CONTROL PILOT for the EVCS 101 to stopdelivering energy at 816. The communications will be validated forcorrectness and the termination of energy delivery verified. The device104 only then terminates TOTAL energy measurement at 817. The device 104will then display the measurement of the total energy delivered by theEVCS 101 on, for example, display 107. The measurement can be manuallycompared by the user against the energy registered on the display 102 ofthe EVCS 101. Alternatively, the data from the EVCS display may be inputto the device 104, after which the device 104 (e.g., with DPM 326)computes the accuracy of the EVCS-generated value(s) by a comparisonwith the values generated by the device 104 itself. The device 104 mayalso verify the billing computation in addition to the accuracy of thetotal energy delivered values. If a GFCI test was selected to be run at818, it may be performed by the device 104 at this point in theoperational sequence. The device 104 may create at 819 and store areport of the complete charging session and test results, display thesame, and be capable of uploading the report/results through one of itscommunication ports.

The biggest advantage of this method is that it is a transactionalmethod where the entire “fuelling” process is checked. The total energydelivered as measured by the device is directly compared to the readingsof the EVCS for both total energy and billing amount. Another advantageof this test sequence is that it does not require an energy pulse outputfrom the EVCS. A possible disadvantage is that it may take acomparatively long time to get sufficient resolution on the EVCS displayfor an accurate measurement with which to compare the total energymeasurement output of the device 104. If the EVCS has a displayresolution of, for example, 0.001 kWh then this will not be an issue.This approach emulates the method used to check gas pumps in that itmeasures the total energy (fuel) delivered in the transaction, similarto measuring the total volume of gasoline delivered in a transaction.

Active Mode, Standard Meter Test (“STANDARD”)

FIG. 8B is a flow diagram for an active mode, standard meter test(“STANDARD”). Energy pulse output is available on the EVCS. For revenuemetering in the normal electric power industry all meters provide aninfrared energy pulse output (ANSI C12.20 Section 4.6). A pulse isoutput each time a specific amount of energy is measured by the EVCS. Insome exemplary embodiments, the device 104 may compare the measurementof energy delivered as determined by the device 104 itself with thenumber of pulse intervals over which the measurement was made. In thisway, a very accurate comparison may be made independent of a display oflimited resolution on the EVCS. This approach may be primarily used byEVCS manufacturing companies since it does not provide a fulltransactional check.

In this mode, the device 104 first establishes a steady state chargingsituation, then measures energy for a fixed number of energy pulses fromthe EVCS, then terminates the charging process. The process begins atstart 801. The user then sets up this mode by interacting with thedevice 104 firmware/software through, for example, the keypad 112 anddisplay 107. The necessary setup information is entered at 802 and mayinclude:

-   -   Select ACTIVE Mode (Device 104 serves as the load for the EVCS        101 or, alternatively, a standalone programmable load 119 is        connected to the secondary port 106 of the device 104.)    -   Select Standard Meter Test (The energy measurement will be made        for a specified number of pulses.)    -   Set Number of pulses (A number of test pulses will be selected.)    -   Set Charging Current (The programmable load 119 is enabled by        the user selecting the charging current for the test.) As an        alternative to the user manually setting a load, the device 104        may operate in an automatic mode (“AUTO”) where it selects the        load to be applied based on the output capability of the EVCS as        encoded in the pilot control signal. Multiple test sequences can        also be setup to allow for testing at a high load (>85% of        maximum) and at low load (<10%) of maximum automatically.    -   Test GFCI (yes or no)    -   Test pilot control diode (yes or no)

The user is instructed to attach the energy pulse pickup 108 to the EVCSat 803. Because the device 104 is set to a STANDARD meter mode, energymeasurement will not start until stable charging conditions have beenestablished. The user is instructed at 805 to insert the EVCS plug 103into the primary port 105 of the device 104. Upon insertion the device104 signals the appropriate levels as determined by J1772-201010 orother applicable standard on the PROXIMITY line 807 and awaits theCONTROL PILOT protocol. The user may have to interact with controls onthe EVCS to initiate the CONTROL PILOT exchange. The instrument verifiesthe PROXIMITY at 806 and generates a start charging state on the CONTROLPILOT 809. If the exchanges were successful the EVCS will startdelivering power. Otherwise, an error will be reported 810. The device104 may adjust the load at 812 if necessary to meet the testingrequirements as specified in the setup. It then verifies that allcharging parameters are within specifications set by J1772-201010 orother applicable standards at 813. If charging parameters are not withinspecifications, an error is reported at 814 and the test is terminated.If all parameters are within expected ranges, then the test is permittedto continue. Energy measurement preferably commences synchronously withthe first pulse after the charging current has been stabilized at 820.Power measurement will continue for the preset number of pulses. Oncethe number of energy pulses reaches the preset limit, the measurement ofenergy will be stopped synchronously with an energy pulse at 821. Atthis point the test is complete, and the device 104 will signal via theCONTROL PILOT for the EVCS 101 to stop delivering energy at 816. Thecommunications will be validated for correctness and the termination ofenergy delivery verified at 816 (e.g., by the digital processing means326). If a GFCI test 818 was selected to be run, it may be performed bythe device 104 at this point in the operational sequence. The device 104may create a test report at 819 that presents the accuracy of themetering of the EVCS as computed by comparison with the energy pulseoutput of the EVCS. The instrument may store a report of the completecharging session and test results, display the same, and be capable ofuploading the results through one of its communication ports.

An advantage of this approach is that a very accurate test of themetering accuracy of an EVCS can be conducted in a very short period oftime that is independent of the resolution of the EVCS display. Adisadvantage of this approach is that it does not measure the totalenergy delivered, i.e. it is not a full transactional verification.Hence, it is not the equivalent to testing a gas pump which verifiesthat when it reads that it has dispensed 5 gallons of gas, precisely 5gallons has been dispensed.

The disadvantages of the two modes above can be addressed through a DUALmode which allows the instrument to do both modes simultaneously.

Active Mode, Dual Energy Test (“DUAL”)

FIG. 8C is a flow diagram for an active mode, dual energy test (“DUAL”).This DUAL mode can be used if the EVCS has an energy pulse output 113.

In this mode the device 104 measures all energy flows from the EVCS fromthe time the EVCS 104 starts to the time charging is completed. However,like the Standard Meter Test mode, it also measures the precise energydelivered during a set number of energy pulses. This permits testingboth total energy delivered and fundamental metering accuracysimultaneously.

The process begins at start 801 and proceeds similar to the Active Mode,Total Energy Test described above. The necessary setup information 802may be very similar to the Active/Total Energy Test mode:

-   -   Select ACTIVE Mode (Device 104 serves as the load for the EVCS        101 or, alternatively, a standalone programmable load 119 is        connected to the secondary port 106 of the device 104.)    -   Select DUAL Test (Both TOTAL and STANDARD tests will be run        simultaneously.)    -   Set Number of Pulses (A number of energy pulses will be        entered.)    -   Set Charging Time (A time to run the test is selected/entered.)    -   Set Charging Current (The programmable load 119 is enabled by        the user selecting the charging current for the test.) As an        alternative to the user manually setting a load, the device 104        may operate in an automatic mode (“AUTO”) where it selects the        load to be applied based on the output capability of the EVCS as        encoded in the pilot control signal. Multiple test sequences can        also be setup to allow for testing at a high load (>85% of        maximum) and at low load (<10%) of maximum automatically.    -   Test GFCI (yes or no)

The user is instructed to attach the energy pulse pickup 108 to the EVCS101 at 803. Energy measurement starts immediately as in TOTAL test modeat 804. The user is instructed at 805 to insert the EVCS plug 103 intothe primary port 105 of the device 104. Upon insertion the device 104signals the appropriate levels on the PROXIMITY line at 807 and awaitsthe CONTROL PILOT protocol. The user may have to interact with controlson the EVCS 101 to initiate the CONTROL PILOT exchange. The device 104verifies the PROXIMITY at 807 and generates a start charging state onthe CONTROL PILOT 809. If the exchanges were successful, the EVCS willstart delivering power. Otherwise, an error may be reported at 810. Theinstrument adjusts the load at 812 if necessary to meet requirements. Itthen verifies that all charging parameters are within specifications at813. If charging parameters are not within specifications, an error maybe reported at 814 and the test terminated. Pulse based energymeasurement will commence synchronously with the first pulse after thecharging current has been stabilized at 823. Pulse based energymeasurement will continue for the preset number of pulses at 824. Oncethe preset measurement time has been reached at 825, the EVCS will besignaled to cease charging at 816 and the termination protocolvalidated. TOTAL energy measurement is then terminated at 817. Theinstrument will display the measurement of total energy delivered by theEVCS which can then be manually compared against the energy registeredon the display of the EVCS. Alternatively, the data from the EVCSdisplay may be input to the device 104, after which the device 104(e.g., with DPM 326) computes the accuracy of the EVCS-generated valuesby a comparison with the values generated by the device 104 itself. Thedevice 104 may also verify the billing computation in addition to theaccuracy of the total energy delivered values. If a GFCI test at 818 wasselected to be run, it may be performed at this point in the operationsequence. The device 104 may create at 819 and store a report of thecomplete charging session and test results, display the same, and becapable of uploading the results through one of its communication ports.

An advantage of this approach is that it makes both a high accuracyenergy pulse based measurement and a TOTAL energy measurement during thesame test run. This provides data analogous to the testing procedureused for ANSI C12 revenue meters and TOTAL energy data analogous to thecurrent gas pump test process.

Passive Mode, Dual Energy Test (“PASSIVE”)

FIG. 8D is a flow diagram for a passive mode, dual energy test(“PASSIVE”). In PASSIVE mode, the device 104 is connected in seriesbetween the EVCS 101 and the electric vehicle 111 as shown, for example,in FIG. 2. In this approach, the device 104 does not activelyparticipate in the charging process. Rather, it monitors all signalspassing between the EVCS 101 and the actual electric vehicle 111.

In this approach the electric vehicle is in complete control of thecharging process. In other words, the device 104 is not in control ofthe charging process. The device 104 may be configured or configurableto measure some or all energy flows to and/or from the EVCS 101 from thetime the EVCS starts delivering energy until the time charging iscompleted. The process begins at start 801. The user then sets up thismode by interacting with the device 104 filmware/software through, forexample, the keypad 112 and display 107. Setup information entered at802 may include one or more of the following:

-   -   Select PASSIVE Mode (The electric vehicle 111 serves as the load        for the EVCS.)    -   Select DUAL Energy Measurement (Both total energy delivered and        pulse based accuracy measurements may be made.)    -   Number of Energy Pulses (The system may automatically use the        maximum number of whole pulse intervals during the period that        the charge current is stable.)    -   Charging Time (This not required to be set in the device 104        since it is controlled by the electric vehicle.)    -   Charging Current (This not required to be set in the device 104        because it is controlled by the electric vehicle.)

The user is instructed to attach the energy pulse pickup to the EVCS at803 if the EVCS has that capability. Energy measurement startsimmediately as in TOTAL energy mode at 804. The user is instructed at805 to insert the EVCS plug 309 into the primary port 105 of the device104. The user is also instructed at 806 to insert one end of cable 109into the secondary port 106 and the other end of the cable 109 into theelectric vehicle connector/port 110. Once the ECVS 101 and the EV 111are connected to the device 104, the EVCS and electric vehicle willexchange PROXIMITY signals. This is monitored by the device 104 at 830.This will be followed by an exchange of the CONTROL PILOT protocol. Thisis also monitored by the device 104 at 831. If an invalid exchange isdetected, then an error report will be generated at 810. While thecharging sequence is running it is monitored for out of specificationoperation at 832 which is reported at 814 if detected. Load current isalso monitored and optionally recorded at 833. Once a stable chargingsituation is reached between the ECVS 101 and the EV 111, a pulse basedenergy measurement will begin on the first energy pulse detected at 834.Pulse based energy measurement will be terminated on the last validenergy pulse received during stable charging at 835. When initiated bythe electric vehicle 111 the termination sequence on the CONTROL PILOTline will be monitored and validated by the device 104 at 836. If a GFCItest was selected to be run, it may be performed at 818 after completingmeasurements for determining power delivered by the EVCS. At 819, thedevice 104 may create and store a report of the complete chargingsession and test results, display the same, and be capable of uploadingthe results through one of its communication ports.

An advantage of this approach is that it makes both a high accuracyenergy pulse based measurement and a TOTAL energy measurement during thesame test run. This provides data analogous to the testing procedureused for ANSI C12 revenue meters and TOTAL energy data analogous to thecurrent gas pump test process. Another advantage is that for highcurrent situations the EV provides the load thus eliminating the issueof very large heat dissipation in a resistive programmable load part ofor attached to the device 104.

Four distinct operational modes for the system have been described.However, because the system is able to detect what connections the userhas made, it is possible for the system to implement an AUTO mode inwhich the system determines what is the most appropriate testmethodology, given the connections the user has made. For example themain unit 104 can detect if the user has connected a programmable load119 to the system. If a programmable load has been connected then thesystem knows it is in ACTIVE mode. It can detect if a pulse pickup 108has been connected, if so it will attempt to use the DUAL ENERGY testmode. This simplifies the use of the equipment.

While exemplary embodiments of the present invention have been disclosedherein, one skilled in the art will recognize that various changes andmodifications may be made without departing from the scope of theinvention as defined by the following claims.

What is claimed is:
 1. A programmable load controller for providing avariable effective load to an electric vehicle charging station (EVCS)using one or more fixed loads connectable thereto, the programmable loadcontroller comprising a chopper circuit including a full wave bridge anda power switching transistor with pulse width modulated control, whereinthe chopper circuit allows the variable effective load as seen by theEVCS to be any of a plurality of different fractions of a maximum loadprovided by the one or more fixed loads, wherein the programmable loadcontroller presents a substantially unity power factor.
 2. Theprogrammable load controller of claim 1, further comprising an isolatedgate driver with two or more pulse transformer circuits which arecoupled together to provide a range of duty cycles with a lower boundbelow 50% and an upper bound above 50% for the pulse width modulatedcontrol.
 3. The programmable load controller of claim 2, wherein therange of duty cycles is from near zero to 100% for the pulse widthmodulated control such that the variable effective load is capable ofbeing varied from near zero to the maximum load provided by the one ormore fixed loads.
 4. The programmable load controller of claim 1,further comprising circuitry at both an input side and output side ofthe chopper circuit to minimize harmonic distortion.
 5. The programmableload controller of claim 1, wherein the power switching transistor is anIGBT.
 6. The programmable load controller of claim 1, wherein thechopper circuit further comprises a snubber for filtering out highvoltage spikes which result from switching the power switchingtransistor.
 7. The programmable load controller of claim 1, wherein theone or more fixed loads to which the programmable load controller isconnectable are selected from at least one of a high wattage heater anda resistor bank.
 8. An instrument for accurately verifying the activeenergy delivered by an electric vehicle charging station (EVCS),comprising: a primary port for receiving a charging cable normallyconnecting the EVCS to an electric vehicle; one or more measuringdevices which simultaneously make sampling measurements of voltage andcurrent from one or more supply lines delivering power from the EVCS toone or more fixed loads via a programmable load controller after thecharging cable has been received at the primary port; digital processingmeans configured to calculate a first value of active energy deliveredby the EVCS to the one or more fixed loads from the samplingmeasurements obtained from the one or more measuring devices; and atleast one output device for displaying or transmitting the first valueof active energy delivered or one or more values determined from thefirst value of active energy delivered for comparison with a meteredvalue of active energy delivered as given by the EVCS.
 9. The instrumentof claim 8, wherein the one or more measuring devices make a firstsampling measurement at or before a start of power transfer through theprimary port and a final sampling measurement at or after an end ofpower transfer through the primary port, the first value of activeenergy delivered being calculated from a continuous stream of samplingmeasurements made over an entire time period from the first samplingmeasurement to the final sampling measurement.
 10. The instrument ofclaim 8, wherein the digital processing means is further configured tomake the comparison of the first value of active energy delivered andthe metered value of active energy delivered.
 11. The instrument ofclaim 10, wherein the at least one output device displays or transmits aresult of the comparison as one of the one or more values determinedfrom the first value of active energy delivered.
 12. The instrument ofclaim 10, wherein the result of the comparison is an indication ofwhether or not a difference between the first value of active energydelivered and the metered value of active energy delivered exceeds apredetermined threshold.
 13. The instrument of claim 10, wherein theresult of the comparison indicates a magnitude by which the first valueof active energy delivered and the metered value of active energy differfrom one another.
 14. The instrument of claim 8, further comprising anenergy pulse pickup connectable to the EVCS to receive pulses indicatingdelivery of one or more fixed quantities of active energy as given bythe EVCS.
 15. The instrument of claim 14, wherein the digital processingmeans is further configured to calculate a second value of active energydelivered over a predetermined number of pulses, the second value ofactive energy delivered being usable to verify EVCS metering accuracy.16. The instrument of claim 15, wherein the digital processing means iscapable of calculating both the first value of active energy deliveredand the second value of active energy delivered during a singleoperational test sequence.
 17. The instrument of claim 15, wherein thesecond value of active energy delivered is usable to verify EVCSmetering accuracy independent of the first value of active energydelivered.
 18. The instrument of claim 8, further comprising a facilityfor testing operation of a ground fault protection of the EVCS.
 19. Theinstrument of claim 8, wherein the one or more output devices includesone or more interfaces for communicating any or all of its test resultsand setup information to a laptop, tablet computer, smart phone,external memory device, or other device.
 20. The instrument of claim 8,further comprising communication means which allow the instrument tocommunicate with the EVCS to determine the performance capability of theEVCS and synchronize operation of the EVCS if the EVCS is capable ofproviding performance information.
 21. The instrument of claim 8,wherein the primary port allows a plurality of different types of EVCSconnectors with different protocols to be accommodated throughinterchangeable connector modules.
 22. The instrument of claim 8,wherein the one or more measuring devices are configured to measure bothenergy delivered by the EVCS to the load and energy delivered to theEVCS from an external source.
 23. The instrument of claim 8, wherein thedigital processing means is further configured to calculate a value ofapparent energy.
 24. The instrument of claim 8, wherein the digitalprocessing means is further configured to calculate a value of reactiveenergy.
 25. The instrument of claim 8, wherein the data processing meanscontains a memory in which the instrument stores site and testinformation for later upload.
 26. The instrument of claim 8, furthercomprising a GPS subsystem usable to identify a test site and accesssite specific information stored in memory.
 27. An electric vehiclecharging station (EVCS) test system for accurately verifying the activeenergy delivered by an EVCS, comprising: a programmable load controllerfor providing a variable effective load to the electric vehicle chargingstation (EVCS) using one or more fixed loads connectable thereto; and ameasuring instrument, comprising a primary port for receiving a chargingcable normally connecting the EVCS to an electric vehicle; one or moremeasuring devices which simultaneously make sampling measurements ofvoltage and current from one or more supply lines delivering power fromthe EVCS to the one or more fixed loads via the programmable loadcontroller after the charging cable has been received at the primaryport; digital processing means configured to calculate a first value ofactive energy delivered by the EVCS to the one or more fixed loads fromthe sampling measurements obtained from the one or more measuringdevices; and at least one output device for displaying or transmittingthe first value of active energy delivered or one or more valuesdetermined from the first value of active energy delivered forcomparison with a metered value of active energy delivered as given bythe EVCS.
 28. The EVCS test system of claim 27, wherein the programmableload controller comprises a chopper circuit including a full wave bridgeand a power switching transistor with pulse width modulated control,wherein the chopper circuit allows the variable effective load as seenby the EVCS to be any of a plurality of different fractions of a maximumload provided by the one or more fixed loads, wherein the programmableload controller presents a substantially unity power factor.
 29. TheEVCS test system of claim of claim 28, wherein the programmable loadcontroller further comprises an isolated gate driver with two or morepulse transformer circuits which are coupled together to provide a rangeof duty cycles with a lower bound below 50% and an upper bound above 50%for the pulse width modulated control.
 30. The EVCS test system of claimof claim 29, wherein the range of duty cycles is from near zero to 100%for the pulse width modulated control such that the variable effectiveload is capable of being varied from near zero to the maximum loadprovided by the one or more fixed loads.
 31. The EVCS test system ofclaim 28, further comprising circuitry at both an input side and outputside of the chopper circuit to minimize harmonic distortion.
 32. TheEVCS test system of claim 28, wherein the power switching transistor isan IGBT.
 33. The EVCS test system of claim 28, wherein the choppercircuit further comprises a snubber for filtering out high voltagespikes which result from switching the power switching transistor. 34.The EVCS test system of claim 28, wherein the one or more fixed loads towhich the programmable load controller is connectable are selected fromat least one of a high wattage heater and a resistor bank.
 35. A methodof providing a variable effective load to an electric vehicle chargingstation (EVCS) using one or more fixed loads connectable thereto,comprising pulse width modulating an input to a power switchingtransistor of a chopper circuit to vary the variable effective load seenby the EVCS to any of a plurality of different fractions of a maximumload provided by the one or more fixed loads.
 36. The method of claim35, wherein the step of pulse width modulating is performed using anisolated gate driver with two or more pulse transformer circuits coupledtogether to provide a range of duty cycles with a lower bound below 50%and an upper bound above 50%.
 37. The method of claim 36, wherein therange of duty cycles is from near zero to 100% for the step of pulsewidth modulating such that the variable effective load is capable ofbeing varied from near zero to the maximum load provided by the one ormore fixed loads.
 38. The method of claim 35, further comprising a stepof power signal filtering with circuitry at both an input side andoutput side of the chopper circuit to minimize harmonic distortion. 39.The method of claim 35, wherein the power switching transistor is anIGBT.
 40. The method of claim 35, further comprising a step of filteringout, with a snubber, high voltage spikes which result from switching thepower switching transistor during the step of pulse width modulating.41. The method of claim 35, wherein the EVCS is connectable to one ormore fixed loads that include at least one of a high wattage heater anda resistor bank.
 42. A method for accurately verifying the active energydelivered by an electric vehicle charging station (EVCS), comprisingsteps of: receiving at a primary port a charging cable normallyconnecting the EVCS to an electric vehicle; making sampling measurementsof voltage and current simultaneously from one or more supply linesdelivering power from the EVCS to one or more fixed loads via aprogrammable load controller after the charging cable has been receivedat the primary port; calculating a first value of active energydelivered by the EVCS to the one or more fixed loads from the samplingmeasurements with a digital processing means; and displaying ortransmitting the first value of active energy delivered or one or morevalues determined from the first value of active energy delivered withat least one output device for comparison with a metered value of activeenergy delivered as given by the EVCS.
 43. The method of claim 42,wherein the step of making sampling measurements includes making a firstsampling measurement at or before a start of power transfer through theprimary port and a final sampling measurement at or after an end ofpower transfer through the primary port, the first value of activeenergy delivered being calculated in the calculating step from acontinuous stream of sampling measurements made over an entire timeperiod from the first sampling measurement to the final samplingmeasurement.
 44. The method of claim 42, further comprising a step ofcomparing the first value of active energy delivered with the meteredvalue of active energy delivered.
 45. The method of claim 43, whereinsaid step of displaying or transmitting includes displaying ortransmitting a result of the comparison as one of the one or more valuesdetermined from the first value of active energy delivered.
 46. Themethod of claim 44, wherein a result of the comparison is an indicationof whether or not a difference between the first value of active energydelivered and the metered value of active energy delivered exceeds apredetermined threshold.
 47. The method of claim 44, wherein a result ofthe comparison indicates a magnitude by which the first value of activeenergy delivered and the metered value of active energy differ from oneanother.
 48. The method of claim 42, further comprising a step ofcalculating a second value of active energy delivered over apredetermined number of pulses received from the ECVS with an energypulse pickup, the second value of active energy delivered being usableto verify EVCS metering accuracy.
 49. The method of claim 48, whereinthe second value of active energy delivered is usable to verify EVCSmetering accuracy independent of the first value of active energydelivered.
 50. The method of claim 42, further comprising a step ofpulse width modulating an input to a power switching transistor of achopper circuit to vary a variable effective load seen by the EVCS toany of a plurality of different fractions of a maximum load provided byone or more fixed loads connectable to the EVCS.
 51. The method of claim50, wherein the step of pulse width modulating is performed using anisolated gate driver with two or more pulse transformer circuits coupledtogether to provide a range of duty cycles with a lower bound below 50%and an upper bound above 50%.
 52. The method of claim 51, wherein therange of duty cycles is from near zero to 100% for the step of pulsewidth modulating such that the variable effective load is capable ofbeing varied from near zero to the maximum load provided by the one ormore fixed loads.
 53. The method of claim 50, further comprising a stepof power signal filtering with circuitry at both an input side andoutput side of the chopper circuit to minimize harmonic distortion. 54.The method of claim 50, wherein the power switching transistor is anIGBT.
 55. The method of claim 50, further comprising a step of filteringout, with a snubber, high voltage spikes which result from switching thepower switching transistor during the step of pulse width modulating.56. The method of claim 50, wherein the EVCS is connectable to one ormore fixed loads that include at least one of a high wattage heater anda resistor bank.